Question

Identify the correct statement from following

• A. Lanthanoids have greater tendency to form complexes than actinoids.
• B. Actinoid contraction is greater than lanthanoid contraction.
• C. Hydroxides of actinoids are less basic than lanthanoid hydroxides.
• D. Binding energy of $4f$-orbitals is lower than $5f$-orbitals.

Hint:

Poor shielding of $5f$-electrons causes stronger actinoid contraction compared to lanthanoid contraction.

Answer 1

The Correct Option is B

Step 1: Understanding contraction effect.
Both lanthanoid and actinoid series show contraction due to poor shielding effect of $f$-electrons, leading to a gradual decrease in atomic and ionic radii.

Step 2: Comparison of shielding.
In actinoids, the $5f$-electrons have even poorer shielding compared to $4f$-electrons of lanthanoids. Additionally, relativistic effects are more prominent in actinoids.

Step 3: Analysis of given statements.
Lanthanoids form fewer complexes than actinoids, actinoid hydroxides are generally more basic, and $4f$-orbitals are more deeply buried (higher binding energy) than $5f$-orbitals.

Step 4: Conclusion.
Hence, the correct statement is (B) Actinoid contraction is greater than lanthanoid contraction.